Inhibition reactivation myofibrillar ATPase technique for demonstration of three fiber types in a single cryostat muscle section.

An inhibition reactivation technique was used for histochemical staining of human skeletal muscle sections. Myofibrillar ATPase activity was inhibited by sodium hydroxymercuribenzoate (2.5 mM in 0.1 M Tris-HCl buffer, pH 7.2-7.5, 30 min) and successively reactivated by cysteine which was added to incubation solution (10 mM cysteine-HCl, 2.5 mM ATP-disodium salt, 50 mM potassium chloride and 27 mM calcium chloride in barbital buffer, pH 9.4, 35 min at 37 C). This technique allows the distinction of three fiber categories with different staining intensities in single cross-section. Dark, intermediate and light fibers correspond to IIB, I, and IIA types, respectively. Storage of air dried sections in the freezer at -20 C for one month had no influence on staining characteristics.